Fish welfare issues are predicated on understanding whether fish are sentient beings. Therefore, we analyzed the logic of the methodologies used for studying this attribute. We conclude that empirical science is unable to prove or to disprove that fish are sentient beings. Thus, we propose a combined ethical-scientific approach for considering fish as sentient beings. The most difficult ongoing question is to determine which conditions fish prefer. Approaches to assess fish preferences should be rigorously and cautiously employed. In light of these considerations, attempts to establish physiological standards for fish welfare are discouraged, and a preference-based definition of fish welfare is proposed.

The effect of chronic social stress on growth, energetic substrates and hormones was tested in rainbow trout, Oncorhynchus mykiss. After a 14-day isolation period, the fish were paired for 8 days. In order to expose fish to chronic intermittent social contact during pairing, they were maintained in direct contact with each other during the first day. After that, a black plastic screen partition was introduced in each tank, preventing direct contact between animals. Every day the partition was removed for 30 minutes, allowing physical interaction between fish. At the end of pairing period, they were isolated again for 13 days. Fish were weighed and blood was sampled frequently during the experiment. Plasma levels of cortisol, growth hormone, glucose, total protein and free amino acids were quantified. Both dominants and subordinates had specific growth rate decreased during the pairing period and but only subordinates increased when the stressor was abolished (dominants: 0.32 ± 0.21 and 0.24 ± 0.41, subordinates: -0.77 ± 0.29 and 0.37 ± 0.31, respectively). Dominants showed a higher cortisol level one week after pairing condition had been abolished than subordinates (dominants: 56.76 ± 13.26, subordinates:31.89 ± 13.36). We conclude that chronic condition of intermittent social stress represents a stressful condition for animals of both hierarchical ranks and a treatment of one daily short direct contact between conspecifics does not promote habituation in fish, as mentioned for other stressors.social stress, energetic of stress, hierarchical dominance, rainbow trout, Oncorhynchus mykiss.

Chemical communication is widely used in aquatic environments, where visual or auditory signals may not be always effective. Fish of the superorder Ostariophysi are known to display epidermal cells (club cells) that produce and store alarm substances, which are released to the water when the skin is damaged. Responses to alarm substances range widely, between active searches for refuge to a complete stop in any locomotor activity. In this study a large number of binucleated club cells (average density of 11 cells /µm 2 ) were histologically observed in the skin of the catfish Rhamdia quelen (known as jundiá). Skin extract (2, 5, and 10% w/v) applied for 15 minutes to conspecifics elicited increase in swimming activity and in the area visited by the fish inside the tank. However, exposure to the epithelial alarm cue did not evoke any stress response: plasma osmolality, ions (sodium, chloride, magnesium, and potassium), glucose and cortisol remained unchanged. In conclusion, the conspecific alarm cue of the jundiá induces behavioral responses but not an acute stress response upon short-term exposure, compatible with its role in fostering physical integrity without representing major stress activation. Considering that in the natural environment such stimuli must quickly disappear due to dilution and that rapid protection responses may be necessary upon the possibility of an approaching predator, a faster mechanism to assure survival may come into play, such as sympathetic nervous system activation.Comunicação química é amplamente utilizada por animais que vivem em ambiente aquático, onde sinais visuais e auditivos nem sempre são facilmente identificados. Os Ostariophysi são conhecidos por apresentarem células club na epiderme, as quais produzem e estocam substância de alarme que são liberadas para o ambiente quando a pele é lesionada. As respostas dos peixes a substância de alarme variam entre exploração ativa por refúgios até a parada completa de atividade locomotora. Neste estudo, grande número de células club binucleadas (densidade média de 11 células/µm2) foram histologicamente observadas na epiderme do jundiá, Rhamdia quelen. Peixes expostos a extrato de pele de conspecíficos (2, 5, e 10% peso/vol) por 15 minutos apresentaram aumento da atividade locomotora e da área de dispersão. No entanto, essa exposição não promoveu nenhuma resposta de estresse -osmolalidade plasmática, íons (sódio, cloreto, magnésio e potássio), glicose e cortisol não sofreram alteração. Concluímos que a exposição aguda a extrato de pele de conspecíficos promovem respostas comportamentais de fuga, que essa espécie apresenta grande concentração de células club, as quais devem estar envolvidas nessas respostas e que a exposição aguda ao estímulo não promoveu respostas bioquímicas indicativas de estresse. Considerando que no ambiente natural tais estímulos devem desaparecer rapidamente dados a diluição do meio e que respostas rápidas de proteção devem ser desencadeadas frente à possibilidade de presença de predador, vias rápidas de suporte ...

resumo -No Brasil, assim como em outras partes do mundo, a preocupação com o bem-estar dos peixes encontra-se em seus passos iniciais. O bem-estar de peixes, se comparado com o bemestar de outras espécies de animais de produção, é um tópico praticamente ausente para consumidores, produtores e legislação vigente. Porém, as evidências anatômicas, fisiológicas, comportamentais, evolutivas e farmacológicas sugerem que os peixes experimentam sentimentos como dor, medo e outros de maneira similar aos demais vertebrados. Isso sugere que os peixes têm potencialmente a capacidade de sofrer e apresentar outros sentimentos, ou seja, que os peixes são seres sencientes. Esta revisão teve como objetivo discutir aspectos referentes à dor e à presença de consciência nos peixes, visando colaborar com o entendimento da senciência nesses animais. Uma vez reconhecida a senciência em peixes, estes animais são incluí-dos nas considerações éticas acerca de não serem submetidos a sofrimento. palavras-chave: Senciência; cognição; consciên-cia; dor; teleósteo.abstract -In Brazil, as well as in other parts of the World, the concern about fish welfare is in its initials steps. Fish welfare, if compared to the welfare of other species of farm animals, is practically an absent topic for consumers, producers and current law. However, anatomic, physiologic, behavioral, evolutive and pharmacologic evidences suggest that fish experience feelings such as pain, fear and others, in ways that are similar to other vertebrates. This suggests that fish are potentially capable of experiencing suffering and other feelings; in other words, that fish are sentient. The objective of this review was to discuss pain and consciousness in fish, in order to collaborate with sentience understanding in these animals. Once fishes are recognized as sentient beings, these animals are then included into ethical considerations regarding the avoidance of suffering infliction.

Bile acids are potent olfactory and gustatory stimulants for fish. Electro-olfactogram recording was used to test whether the olfactory epithelium of pintado catfish Pseudoplatystoma corruscans is specifically sensitive to bile acids, some of which have been hypothesized to function as pheromones. Five out of 30 bile acids that had been pre-screened for olfactory activity in fish were selected. Cross-adaptation experiments demonstrated that sensitivity to bile acids is attributable to at least 3 independent classes of olfactory receptor sites. The taurocholic acid (TCA) and taurochenodeoxycholic acid (TCD) were the most potent compounds. By using avoidance/preference tests, we found that P. corruscans prefers water containing TCA. Bile acids are discriminated by olfactory epithelium of pintado, supporting that these compounds could function as pheromones.Os ácidos biliares são potentes estimulantes olfatórios e gustatórios em peixes. Registros em eletro-olfactograma foram usados para testar se o epitélio olfatório de Pseudoplatystoma corruscans, pintado, é sensível aos ácidos biliares, alguns dos quais têm sido propostos como feromônios. Foram selecionados cinco de uma lista de trinta ácidos biliares previamente testados em atividade olfatória em peixes. Testes de adaptação cruzada demonstraram que a sensibilidade aos ácidos biliares se dá por 3 classes independentes de sites de receptores olfatórios. O ácido taurocólico (TCA) e o ácido tauroquenodesoxicólico (TCD) foram os compostos mais potentes. Em testes de evasão/preferência, P. corruscans prefere água contendo o ácido TCA. Os ácidos biliares são discriminadas por epitélio olfatório de pintado, evidenciando que estes compostos podem funcionar como feromônios.